The present invention relates to a Raman laser that is used as a pump light of the optical amplifier in high-capacity long-distance optical communication network. In particular, the Raman laser in accordance with an embodiment of the present invention has simple structure and achieves high performance.
As high-powered lasers like Ytterbium doped optical fiber laser has been developed, Raman laser that uses the high-powered lasers as the pump light is known as an important technology to obtain high-powered laser through wide wavelength range.
Especially, regarding ultra optical wavelength technologies of 1.4 xcexcmxcx9c1.6 xcexcm, high-powered lasers that are able to operate in wide wavelength range are very useful as a pump light of optical fiber Raman lasers. The ultra optical wavelength technologies utilize low loss wavelength range for tens of tera bit range optical communications.
Currently, in S-band of 1.49xcx9c1.53 xcexcm, appropriate material is not found for optical fiber amplifier and therefore importance of Raman amplifier is well known. However, a pump laser light source for high-powered operation has not been proposed yet.
Conventional optical fiber cascaded Raman lasers utilize an optical fiber bragg grating and implement a Raman resonator of stoke frequency shifted. This method employs two optical fiber bragg gratings that have maximum reflection ratio regarding stoke frequency shifted wavelength and the two terminals of the optical fibers have nonlinear Raman effect. Also, the two optical fiber bragg gratings illustrate high transparent ratio for other wavelengths to implement intra cavity. Therefore, this method has high conversion efficiency and narrow bandwidth output wavelength.
However, this method requires 2n+1 optical fiber bragg gratings for light of nth order stoke frequency shifted wavelength since a bragg grating and two optical fiber bragg gratings that reflect pump light source are required for each order stoke frequency shifted wavelength.
Therefore, as order of stoke frequency shifted wavelength increases, a number of required optical fiber bragg grating also increase, which causes high cost and serious level of complexity. Also, since the conventional methods employs only optical fiber bragg gratings, Raman lasers in accordance with the conventional methods are not stable. The reason for this disadvantage is that an optical fiber bragg grating is sensitive with environmental variables such as intensity and temperature of pump light source.
An optical fiber cascaded Raman laser scheme is provided. An optical fiber cascaded Raman laser scheme in accordance with an embodiment of the present invention includes a pump light source, an optical fiber, a wavelength division multiplexing optical fiber combiner, another wavelength division multiplexing optical fiber combiner, a short period optical fiber bragg grating, a long period bragg grating, first means, and second means. The pump light source generates pump light. The optical fiber causes Raman scattering regarding the optical pump light as nonlinear material. The wavelength division multiplexing optical fiber combiner forms intra cavity regarding light of second order stoke frequency shifted wavelength. The light is stoke frequency shifted by Raman scattering of the optical fiber. The another wavelength division multiplexing optical fiber combiner forms intra cavity regarding light of first and third order stoke frequency shifted wavelength. The light is stoke frequency shifted by Raman scattering of the optical fiber. The short period optical fiber bragg grating selects and reflects fourth stoke frequency shifted wavelength of output wavelength in intra cavity. The intra cavity is formed by the wavelength division multiplexing optical fiber combiner. The long period bragg grating causes loss on fifth order stoke frequency shifted wavelength and prevents oscillation. The fifth order is next order of output wavelength of the intra cavity. The first means passes pump light emitted from the pump light source and reflects light of fourth order stoke frequency shifted output wavelength. The first means is connected between the pump light source and the wavelength division multiplexing optical fiber combiner. The second means reflects pump light emitted from the pump light source and passing light of output wavelength.
Preferably, the first means comprises a wavelength division Sagnac loop mirror and the second means comprises a short period optical fiber bragg grating having maximum reflection ratio regarding the pump light.
Preferably, the first means comprises a short period optical fiber bragg grating and the second means comprises a short period optical fiber bragg grating having maximum reflection ratio regarding the pump light.
Preferably, the first means comprises a wavelength division Sagnac loop mirror and the second means comprises a wavelength division Sagnac loop mirror.
An optical fiber cascaded Raman laser scheme is provided. An optical fiber cascaded Raman laser scheme in accordance with an embodiment of the present invention includes a pump light source, an optical fiber, a wavelength division multiplexing optical fiber combiner, a short period optical fiber bragg grating, a long period bragg grating, first means, and second means. The pump light source generates pump light. The optical fiber causes Raman scattering regarding the optical pump light as nonlinear material. The wavelength division multiplexing optical fiber combiner forms intra cavity regarding light of first and third order stoke frequency shifted wavelength. The light is stoke frequency shifted by Raman scattering of the optical fiber. The short period optical fiber bragg grating selects and reflects second stoke frequency shifted wavelength of output wavelength in intra cavity. The intra cavity is formed by the wavelength division multiplexing optical fiber combiner. The long period bragg grating causes loss on third order stoke frequency shifted wavelength and prevents oscillation. The fifth order is next order of output wavelength of the intra cavity. The first means passes pump light emitted from the pump light source and reflects light of second order stoke frequency shifted output wavelength. The first means is connected between the pump light source and the wavelength division multiplexing optical fiber combiner. The second means reflects pump light emitted from the pump light source and passes light of output wavelength.
Preferably, the first means comprises a wavelength division Sagnac loop mirror and the second means comprises a short period optical fiber bragg grating.
Preferably, the first means comprises a short period optical fiber bragg grating and the second means comprises a short period optical fiber bragg grating.
Preferably, the first means comprises a wavelength division Sagnac loop mirror and the second means comprises a wavelength division Sagnac loop mirror.